Dr. Lisa Schimmenti is a pediatrician who has completed a three year fellowship in Genetics and metabolism at the University of Minnesota and has received a faculty appointment in Pediatrics at the University of California, Los Angeles as an Assistant Professor. Through the support of this award, the candidate plans to develop an independent laboratory program in red cell developmental disorders. The proposed research will be carried out under the mentorship of Edward R.B. McCabe, M.D., Ph.D., Chairman of pediatrics. The research will be conducted in the laboratories of the Department of pediatrics at UCLA with support for sequencing, synthesis of oligonucleotide primers and tissue culture through the Pediatric Core Facility. The department of Pediatrics at UCLA is committed to Dr. Schimmenti's development as an independent researcher through provision of protected research time and use of the Department's resources. This award will enhance the candidate's potential for success by providing support for investigations into the pathogenesis of erythroleukemia as a model system for abnormal red cell development. Molecular events leading to abnormal red blood cell development and manifesting clinically as erythroleukemia are poorly understood. In normal red cell development, interaction of Erythropoietin (Epo) with the Erythropoietin Receptor (EpoR) is necessary for survival, proliferation and differentiation of erythroid precursors. Disorders of red cell development such as familial polycythemia and erythroleukemia have been associated with mutations in the EpoR gene. Abnormalities in the gene encoding the EpoR have been described in both murine and human erythroleukemia cell lines. in order to better understand the molecular process underlying abnormal red cell development in erythroleukemia, we propose to study an abnormal EpoR occurring in a human erythroleukemia cell line, TF-1. As a consequence of a chromosomal translocation at 19p13.3, one copy of the EpoR gene in TF-1 cells has undergone a deletion in the last exon which is replaced by a novel sequence resulting in a fusion mRNA. This abnormal message is highly expressed and is translated into a truncated receptor protein presumably deleting the C-terminal portion of the EpoR and replacing it with novel sequence. It has been shown that the C-terminus of the EpoR is an important regulatory domain which is lacking in both TF-1 cells and in familial polycythemia. Since patients with familial polycythemia do not develop erythroleukemia, we hypothesize that the fusion of the EpoR gene to an unknown fusion partner gene is one of the molecular changes necessary to promote abnormal clonal proliferation of erythroleukemia cells in the TF-1 cell line. In order to test this hypothesis, we propose three. Specific Aims 1) The EpoR fusion partner gene will be cloned and sequenced; 2) the wild type EpoR cDNA and EpoR fusion cDNA constructs will be transfected into a cytokine dependent cell line and assayed for functional changes in Epo response; 3) Patients with erythroleukemia will be screened for the presence of acquired abnormalities of the EpR and the fusion partner. This project is important to further understand the molecular mechanisms underlying abnormal red cell development and may be generalizable to understanding the molecular pathogenesis of erythroleukemia.